Iraqis voted Saturday to approve or reject a proposed constitution. The polls opened at 7 a.m., just hours after an unknown group has sabotaged power lines in the northern part of the country, plunging the Iraqi capital into darkness and cutting off water supplies.

On Saturday, Iraqi soldiers and police protected polling stations at schools, and driving was banned to stop suicide car bombings. With little violence, turnout was more than 66 percent in the three most crucial provinces. Some 9 million Iraqis cast ballots, election officials said, announcing a preliminary turnout estimate of 61 percent.

President Jalal Talabani and Prime Minister Ibrahim al-Jafaari were shown live on Al-Iraqiya television voting in a hall in Baghdad's heavily fortified Green Zone, where parliament and the U.S. Embassy are located. "The constitution will pave the way for a national unity," said al-Jafaari, according to the AP. "It is a historical day, and I am optimistic that the Iraqis will say 'yes.'"

Iraqis remain divided over the draft constitution. The country's Shiite majority - some 60 percent of its 27 million people - and the Kurds - another 20 percent - support the charter, which provides them with autonomy in the regions where they are concentrated in the north and south. The Sunnis are likely to reject the document.

All voters marked their paper ballot "yes" or "no" under one question, written in Arabic and Kurdish: "Do you agree on the permanent constitution project?" Voters then had the forefinger of their right hands marked with violet ink to prevent multiple voting.

The results of the referendum should be known within three days at most, chief electoral official Adil al-Lami revealed on Saturday.

There were also attacks on the day of the vote. A roadside bomb went off near a polling station in western Baghdad as it opened, injuring two policemen, officials said. U.S. troops exchanged fire with gunmen in Ramad. South of Basra, three armed men attacked an empty polling station at 3 a.m.; the three were arrested, police said.

Three Iraqi troops were killed and three wounded in a roadside bomb attack just hours before voting commenced.

The incident took place near the town of Al-Sahedia, which lies northeast of Baghdad close to the Iranian border, as the soldiers were inspecting polling stations.

West of Baghdad, a civilian was killed during an attack on police near a polling station, and a woman was injured by police in a separate incident as policemen fired at a suspicious vehicle.